The present invention relates to a particular novel class of polysiloxane-polyoxyalkylene copolymers and their use in the formation of cellular urethane products, particularly flexible urethane foam including flame-retarded foam.
It is well known that the urethane linkages of cellular urethanes are formed by the exothermic reaction of a polyfunctional isocyanate and a polyfunctional active hydrogen-containing compound in the presence of a catalyst, and that the cellular structure is provided by gas evolution and expansion during the urethane-forming reaction. Illustrative of suitable active hydrogen-containing compounds are polyether polyols and polyester polyols. In accordance with the "one-shot" process which is the most widely used industrial technique, direct reaction is effected between all of the raw materials which include the polyisocyanate, the active hydrogen-containing compound, the catalyst system, blowing agent and surfactant. A major function of the surfactant is to stabilize the urethane foam, that is, prevent collapse of the foam until the foamed product has developed sufficient gel strength to become self-supporting. Among the various types of silicon-containing compositions reported in the literature as effective stabilizers of urethane foam derived from a polyester polyol and a polyether polyol are those described in U.S. Pat. No. 3,594,334 and Reissue Pat. No. 27,541, respectively. From the standpoint of potency and quality of foam product, especially effective foam stabilizers described in these patents are those in which silicon of the siloxane portion of the respective copolymer components is substituted with methyl groups only.
In recent years considerable effort has been expended and continues, to reduce the recognized objectionable characteristic of urethane polymers in their ability to ignite readily and burn with an open flame. One approach to this problem is to include a flame-retarding agent such as various phosphorus and/or halogen-containing compounds as a component of the foam-producing reaction mixture, and in this respect, to develop improved and more efficient flame-retarding agents. An associated problem is to provide surfactants which not only function to stabilize flame-retarded foam but which also allow for the formation of flame-retarded foam of reduced burning extent relative to surfactants designed for stabilization of non flame-retarded flame. For example, the polymethylsiloxane-polyoxyalkylene copolymers described in the aforementioned patents are excellent stabilizers of non flame-retarded and are also capable of stabilizing flame-retarded foam. However, the flammability properties of the flame-retarded foam products appear to indicate an adverse effect of the surfactant on flame-retardant efficiency.
It is desirable, therefore, and is a principal object of this invention to provide a new class of polysiloxane-polyoxyalkylene copolymers which, in addition to the ability to stabilize non-flame-retarded cellular urethanes, offer particular utility as stabilizers of flame-retarded products.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.